The Metonic cycle is named for Meton, a 5th-century BCE astronomer from Athens who pinpointed this lunar repetition. Every nineteen years, the Moon returns to the same phase, sign, degree, and declination on the same day of the month, with near exact precision. For example, here are the dates of several Full Moons on or near Winter Solstice (bonus: each of these examples features a lunar eclipse):
December 21, 1991: Moon nearly to Taurus/Gemini cusp, at 23º 58' N declination
December 21, 2010: Moon nearly to Taurus/Gemini cusp, 23º 32' N
December 21, 2029: Moon on Taurus/Gemini cusp, 22º 24' N
December 20, 2048: Moon on Taurus/Gemini cusp, 22º 11' N60
That's calendar-cool, but the Moon's other cycle is far trickier.
Imagine that your tribe does a ritual each month to greet the Full Moon as it rises. One evening, somebody says: "Whoa, wasn't the Full-Faced Goddess on the other side of that standing stone last month?" People then notice that it takes years for the Moon to rise on the other side of that standing stone again.
The ancestors were intrigued. They teased out the patterns of the Moon's wandering and then marked it in incredibly creative ways. Given the resulting art and architecture—much of which has only been recognized as lunar-related in recent decades—we can see that honoring the Moon's motion mattered to them a great deal.
While the Sun is steady on its ecliptic path, the Moon meanders. Sometimes her path lies north of the Sun and sometimes south, zigzagging back and forth across the Sun's steady route. This slow-dance pattern of Sun and Moon plays out over an 18.6-year cycle. We see the Sun's extreme north and south points in the solstices. The Moon echoes the Sun's motion and then some, complete with its own solstice-like "standstill"—a multi-month "pause" as it repeatedly hits its extreme positions.
The Sun's Summer Solstice position is 23º 26' N; its Winter Solstice position is 23º 26' S. That's the Sun's yearly range. But the Moon swings back and forth north-to-south each month. During the maximum period of its 18.6-year cycle, the Moon's position throughout each month ranges from about 29º S to about 29º N. These points are called the Moon's north or south maximum extremes, or major standstills. For around a year, most months will show these wide swings to either side of the ecliptic, as the rising Moon shifts radically back and forth nearly 60º along the horizon every two weeks. The small Moon symbols used in figure 82 are just that, no more. Here, phases aren't marked, other than Full or New for the eclipses, since Moon phases are independent of this north-to-south extreme cycle.
Midway through that 18.6-year cycle—at about 9.3 years—the Moon reaches its minimum phase, swinging only from about 18º S to 18º N each month (see figure 83). These points are the Moon's minimum extremes, also called north and south minor standstills.63 Putting "minimum" together with "extreme" may sound contradictory, but it just means that these are the Moon's most extreme positions in the years when it has the least north-south movement. That's far more bouncing around than the Sun does, but much less Moon variation than in the lunar maximum years.
As with the Sun's angles in figure 19, how extreme these lunar separations look to you will depend on your own north-to-south location.
Figures 82 and 83 both show eclipses that occur when a Full or Dark Moon meets the Sun along the ecliptic. Sun, Moon, and Earth must be exactly in line for a solar eclipse. For a lunar eclipse, the order changes to Sun, Earth, and Moon.
Phases, Extremes, and Solstices
Often, the literature on lunar extremes focuses on solstices and Full Moons, which is misleading. Lunar extremes aren't just Full Moon events, or just solstice events. When the Moon is in an extreme phase of its 18.6-year cycle—at year 9 or year 18—it will reach very near its most extreme point repeatedly throughout that year. For example, figure 82 shows the maximum extremes during March 2006, at 28º41' N and 28º43' S. But it hit those same extreme points again in September 2006 (for two more eclipses) and stayed within 1/2º of those numbers from March 2005 until October 2007. That's thirty-one months. Remember, this is called a lunar standstill, as the Moon returns repeatedly to the same extreme positions. This is not a one-night, or even one-month, phenomenon.
If the temple of your hypothetical tribe were aligned to the extremes of the Moon and had any wiggle room at all, you would see several moonrises or moonsets in the key spot during those months, perhaps even some Full Moons. The 18.6-year cycle doesn't affect the Moon's phases, but phases affect visibility. Thus it's nearly impossible to see a New Crescent rising since it's right below the rising Sun, but you may see the same New Crescent set since the Sun's setting has preceded it.
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